As is known, diamond materials exhibit outstanding physical properties including, but not limited to: exceptional hardness; excellent thermal conductivity; high electrical resistance; chemical inertness; high optical transmissiveness; high electrical carrier mobility; and high dielectric breakdown strength. For these reasons, efforts have been made to synthesize diamond and optimize its growth conditions. For example, diamond powders are useful as abrasives, diamond films are useful as optical windows, and diamond coatings are useful to enhance the utility of cutting tool inserts.
Various techniques are known for synthesizing (fabricating) diamond material (e.g., crystals) from carbon, including: high-pressure, high-temperature (HPHT) techniques; conventional flame; torch; alternating current (AC) and direct current (DC) arc; arc jets; hot filament; radio-frequency (RF) chemical vapor deposition (CVD); electron-cyclotron resonance (ECR) enhanced CVD; supersonic beam; ion beam; laser ablation; and laser plasma-assisted synthesis techniques.
As used herein, a "diamond material" includes both diamond (carbon primarily in the sp3 configuration) and "diamond-like carbon" (DLC) (carbon in the sp2 and sp3 configurations).
Generally, for example, CVD processes are used for depositing diamond and DLC films on a substrate (e.g., on a cutting tool insert), and require a vacuum chamber in which to carry out the process, preheating the substrate and a carbon-containing gas, and result in relatively low rates of deposition. There are a number of basic CVD deposition processes currently in use, for depositing diamond coatings. Generally, these processes involve dissociation and ionization of hydrogen and methane precursor gases, which are then passed over and deposited onto a heated substrate. In DC plasma CVD, a DC arc is used to dissociate the precursor gases, and can provide higher gas temperature and energy than most other prior art processes. Microwave CVD uses microwaves to excite the precursor gases, resulting in deposition rates of several microns per hour. Another coating process, related to CVD, is Physical Vapor Deposition (PVD). In PVD, a target in a vacuum chamber is evaporated, as opposed to introducing a gas to the vacuum chamber with CVD. Generally, in any process of fabricating diamond material that requires the use of a vacuum chamber, the size of the substrate that can be coated is limited by the size of the vacuum chamber in which the process is carried out. Generally, in most known processes of fabricating diamond material, the rate of fabrication is relatively low (i.e., the process time is relatively high), and often the process results in the formation of DLC only, containing SP.sup.2 and/or SP.sup.3 configurations and non-diamond carbon phases (e.g., graphite).
These and other limitations of the prior art are addressed by the techniques of the present invention, which do not depend upon a vacuum environment and which do not require the use of a precursor gas.